Compacting work machines are commonly employed for compacting freshly laid asphalt, soil, and other compactable substrates. For example these work machines may include plate type compactors or rolling drum compactors with one or more drums. The drum type work machines function to compact the material over which the machine is driven. In order to more efficiently compact the material the drum assembly often includes a vibratory mechanism for inducing vibratory forces on the material being compacted.
It is common practice in the compacting of asphalt to use work machines that include two rotating drums to more efficiently compact the material. Double drum compactors are used so that during each pass over the material being compacted each drum performs a portion of the compacting process. These double drum compactors either have an articulating frame or each drum has the ability to pivot about a vertical axis so that the work machine can be steered in a desired direction during operation. During tight turning operations the portion of the drum that is radially outward of the turn can slide over the material being compacted. This sliding can cause a tear in the material because the portion of the drum that is radially outward of the turn desires to rotate faster than the inner portion. On the other hand the inner portion of the drum can plow or mound the asphalt because the tendency is for the inner portion of the drum to rotate slower than the outside portion. Both of the above-described tendencies are contrary to the goal of finishing a road surface that is smooth and flat.
A solution in an attempt to minimize the problem set forth above is to provide a drum that has first and second drum sections known as a split drum. The split drum divides the width of a given drum in half allowing an outer drum section to rotate faster than an inner drum section during turning operations. Split drum designs are known in the art and often use a fixed friction pack to couple the two drum sections to one another, such as seen in a Hamm Operating and Service Manual (DV-6, Edition 04 83). This reference teaches having an offset support arrangement wherein the friction pack is offset to one side and the vibratory mechanism is offset to the other side. This imbalance in the drum and results in poor compacting on one side and not the other. Additionally, the frictional force of the friction packs must be overcome however before slip can occur between the drum sections. In operation however these split drums do not always operate in a predictable manner and slip between the sections occurs when not desired and often does not occur when slip is desired. Another attempt to address this problem is disclosed in U.S. Pat. No. 5,390,495 granted on Feb. 21, 1995 and assigned to Poclain Hydraulics. This patent teaches having first and second drum sections that are coupled together by a brake arrangement and using independent drive motors to propel each drum section.
The present invention is directed at overcoming one or more of the problems as set forth above.